Mechanical linkage system

ABSTRACT

A movable hand grip system is disclosed having a plurality of interconnected members which may be adjustably interlocked in three configurations to vary the manner in which an operator can manipulate the hand grip. The system comprises a lever arm forming one leg of a four bar linkage, which is adapted to articulate in three motion modes while imparting a reciprocating motion to an output member. A hand grip is mounted on the lever arm. In a first configuration, the four bar linkage is pivotably supported to a base at the uppermost corner of the quadrilateral oppposite the lever arm. The legs of the four bar linkage are then angularly locked with respect to each other to enable the hand grip and the fixed quadrilateral to pivot about the base support axis. This angular movement of the hand grip can be accomplished by the operator by moving his arm and hand to and fro. In a second configuration, the legs of the four bar linkage are unlocked with respect to each other, while the leg of the quadrilateral opposite the lever arm is locked to the base. This arrangement enables the hand grip to move up and down with respect to the base. This vertical movement of the hand grip can be accomplished by the operator by manipulating his hand about an imaginary axis through the wrist of the operator. In the third configuration, the linkages, including the lever arm, are locked to the base to be secured against any pivoting movement. The hand grip is then unlocked at one attaching point to enable the hand grip to pivot about the lever arm. This angular movement of the hand grip can be accomplished by the operator by manipulating his hand about an imaginary axis through the palm of the operator&#39;&#39;s hand.

United States Patent [191 Buscher et al.

[ Oct. 16, 1973 MECHANICAL LINKAGE SYSTEM [75] Inventors: Richard G.Buscher, Woodland Hills; Richard L. Davis, Pacific Palisades; EdwardKazmarek, Reseda; Richard K. Larsen, La Habra, all of Calif.

Lear Siegler, Inc., Santa Monica, Calif.

[22 Filed: Dec. 30, 1971 [21 Appl; No.: 214,489

[73] Assignee:

2/ 1970 Dinnendahl 74/469 Primary ExaminerMilton Kaufman Attorney-HaroldL. Jackson et al.

[57] ABSTRACT A movable hand grip system is disclosed having a pluralityof interconnected members which may be adjustably interlocked in threeconfigurations to vary the manner in which an operator. can manipulatethe hand grip. The system comprises a lever arm forming one leg of afour bar linkage, which is adapted to articulate in three motion modeswhile imparting a reciprocating motion to an output member. A hand gripis mounted on the lever arm. In a first configuration, the four barlinkage is pivotably supported to a base at the uppermost corner of thequadrilateral oppposite the lever arm. The legs of the four bar linkageare then angularly locked with respect to each other to enable the handgrip and the fixed quadrilateral to pivot about the base support axis.This angular movement of the hand grip can be accomplished by theoperator by moving his arm and hand to and fro. In a secondconfiguration, the legs of the four bar linkage are unlocked withrespect to each other,'while the leg of the quadrilateral opposite thelever arm is locked to the base. This arrangement enables the hand gripto move up and down with respect to the base. This vertical movement ofthe hand grip can be accomplished by the operator by manipulating hishand about an imaginary axis through the wrist of the operator. In thethird configuration, the linkages, including the lever arm, are lockedto the base to be secured against any pivoting movement. The hand gripis then unlocked at one attaching point to enable the hand grip to pivotabout the lever arm. This angular movement of the hand grip can beaccomplished by the operator by manipulating his hand about an imaginaryaxis through the palm of the operators hand.

27 Claims, 9 Drawing Figures [Milli].

1 MECHANICAL LINKAGE SYSTEM BACKGROUND OF THE INVENTION 1. Field of theInvention The present invention relates generally to control systems andmore particularly to mechanical linkage systems for transmitting themovement of an input member through the linkages to an output member.

2. Description of the Prior Art There are many ways of transmittingcommand outputs to control systems. These systems are usually classifiedaccording to the transmission medium utilized, e.g. electrical,mechanical, hydraulic, pneumatic, or any combination thereof.

A commonly used mechanical transmission system utilizes a pivoting leveras an input component which is connectable to mechanical linkages,cables, or the like for transmitting an output command. Such leversystems are utilized to operate cranes helicoptors, fixed wing aircraft,and countless other devices.

In many applications, it is quite advantageous to locate the lever infront of an arm rest to enable the operator to manipulate the lever witha minimum of hand and arm movements. Systems of this nature are known asside arm controllers. Various types of side arm controllers have beenproposed and/or developed for translating the pivoting motion of thehand lever to an output control element. These various types arecatagorized according to the hand and arm movements an operator has tomake in manipulating the hand lever. The particular type of hand andwrist movement depends on the movement of the hand lever and the axisabout which it pivots. If the lever is pivoted about a base support axisbelow the arm rest, the operators hand and arm must move to and froalong the arm rest to actuate the lever. If the hand lever is moved upand down, the operator can drive the lever with his hand by pivoting itabout an imaginary axis located at his wrist. If the hand lever ispivoted about an axis extending through the lever, the operator candrive the lever with his hand by pivoting it about an imaginary axislocated at his palm.

The type of hand movement utilized depends on the operators preference.These preferences are given serious consideration because the smallincremental movements of the hand levers are quite often critical andhighly sensitive, and if the operator has a better feel and receives abetter responsev from one type of movement, it would be highlyadvantageous for him to use it.

The problem encountered with the above is that present day side armcontrollers can operate in only one mode. If a new operator of a machinedesires a side arm controller having a different mechanical movement,the present unit in the machine has to be taken out and the desired unitinstalled, or several units must be installed permanently in themachine. In many applications, because it is highly advantageous toensure that the operator is able to use the type controller that helikes, separate units are kept on hand for each control system.

This, of course, creates a redundancy in equipment, and raises theoperating costs of such systems.

SUMMARY OF THE INVENTION The present invention obviates theabove-mentioned shortcoming by providing a mechanical linkage systemthat is capable of being articulated in a variety of modes toaccommodate a variety of hand movements.

The primary advantage of the present invention is that since the systemis adjustable, only one unit is necessary for each control system. This,of course, greatly reduces the equipment and inventory needed inoperating the machines control systems. As a result, the cost inoperating such systems is substantially reduced.

Another advantage of the present invention is that these adjustments canbe made quite easily, either by the operator or the mechanic, to afforda quick changeover whenever necessary.

The features of the present invention which are believed to be novel areset forth with particularity in the appended claims. The presentinvention, both as to its organization and manner of operation, togetherwith further objects and advantages thereof, may best be understood byreference to the following description, taken in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a sidestick controller having a mechanical linkage system in accordance to thepresent invention; I

FIG. 2 is an elevational view of the linkage system of the presentinvention;

FIG. 3 is an elevational view of the linkage system shown in its firstconfiguration;

FIG. 4 is an enlarged sectional view of the linkage system taken alonglines 4-4 of FIG. 3;

FIG. 5 is an enlarged fragmentary view of the connecting bar utilized inlocking the linkage system in the first configuration;

FIG. 6 is an elevational view of the linkage system shown in its secondconfiguration;

FIG. 7 is an enlarged sectional view of the linkage system taken alonglines 7-7 of FIG. 6;

FIG. 8 is an enlarged sectional view of the linkage system shown in itsthird configuration; and

FIG. 9 is an enlarged sectional view of the linkage system taken alonglines 9-9 of FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings,FIG. 1 illustrates a side stick controller, generally indicated by arrow10, comprising an outer casing 11 having an arm rest 13 mounted on thetop side thereof. The forward top side of the casing 11 further has ahand grip 15 extending outwardly therefrom. As will be describedhereinafter, the hand grip 15 is pivotally mounted within the casing 11.A bellows covering 17 is provided to extend over the front top side ofthe casing 11 in order to protectively cover that portion while stillenabling the hand grip 15 to freely pivot. The entire side armcontroller 10 is especially adaptable to be installed as a unit on theside of the operators seat. The output connectors are adapted to beconnected through the bottom of the casing 11 (not shown) in aconventional manner and do not form a part of the invention.

Referring now to FIG. 2, the hand grip 15 is adapted to be operativelyconnected to a mechanical linkage system, generally indicated by arrow20, which is enclosed within the casing 11.

The linkage system 20 comprises a four bar linkage forming aquadrilateral. The quadrilateral comprises a lever arm 21 forming theone side thereof. The upper extremity of the lever arm 21 pivotallysupports the hand grip 15 about a first axis A. The lever arm 21 is alsopivotally connected to two adjoining legs 23 and 25 which, in turn, areconnected to a leg 27 opposite the lever arm 21 to complete thequadrilateral. These four connections shown are made with conventionalpivot pins 28, 29, 30, and 31.

The four bar linkage is adapted to be pivotally supported from a baseplate 33 through the pivot pin 30. For descriptive purposes, this pivotpoint 30 will be described hereinafter as a second axis B. The baseplate 33 is supported by two side plates 34 and a rear plate 35 which,in turn, are mounted on the bottom plate of the casing 11.

A right angle connecting bar 36 (more clearly shown in FIG. ispositioned at the pivotally supported corner to interconnect the legs 23and 27. This is accomplished by means of connecting elements 37 and 39extending through mating bores formed in the respective components. Theconnecting element 37 is preferably permanently attached to the leg 23and the bar 36, while the connecting element 39 is adapted to beremovably attached to the leg 27 and the bar 35. For this reason, theconnecting element is in the form of a thumbscrew. When not attached tothe bar 36, the thumbscrew 39 preferably remains supported in the boreformed in the leg 23. (See FIG. 7).

An output element 40 is mounted beneath the base plate 33. The rearextremity of the output element 40 extends through a bore formed in therear plate 35 to be slidably supported thereby. The front extremity ofthe output member 40 forms a bore to enable the element 40 to beattached to the connecting bar 36. A bore is also formed on theconnecting bar 36 to enable the two components to be interconnected bymeans of a connecting element 41. (See FIG. 5). The connecting element41 is adapted to be removably attached thereto to enable the outputelement 40 to be disconnected and attached to a hand grip extension 43described hereinafter. I

The extension 43 (more clearly shown in FIGS. 8 and 9) is adapted toextend along the lever arm 21 and is adapted to be removably attachedthereto by means of a thumbscrew 45, extending through mating boresformed in the two components. When notin connection, the thumbscrew 45is supported within the bore formed in the lever arm 21 to enable thehand grip and extension 43 to pivot about axis A. The extension 43 alsoincludes a bore 47 which is utilized for connection to the forwardextremity of the output element 40.

As more clearly shown in FIG. 6, a flange 49 is integrally connected tothe base plate 33 and one of the side plates 34. The flange 49 includesa bore formed therein which is adapted to register with a mating boreformed in the leg 27 for removably receiving a thumbscrew 51. Thethumbscrew 51 functions to fixedly connect the leg 27 to the flange 49.When the two components are not interconnected (as shown in FIG. 4), thethumbscrew 51 is supported within the bore of the flange 49. I

The lever arm 21 and the leg also include additional bores 53 and 55respectively to enable the lever arm 21 and leg 25 to be interconnectedby the pivot pin 29 at various locations. In this manner, the effectivelengths of either leg can be varied to change the configuration of thequadrilateral. FIG. 2 shows the pivot pin 29 connecting the lever arm 21to the leg 25 through the bore 55 to shorten the length of leg 27 andchange the attitude of the lever arm 21. This position is shown inbroken lines.

OPERATION The side arm controller 10 of the present invention is adaptedto be adjustably interlocked to enable the linkage system 20 to beoperated in three configurations to impart a reciprocating motion to theoutput element 40. These three configurations function to enable thehand grip 15 to be articulated in three modes to accommodate any of thebasic hand and arm movements an operator can make.

The first configuration is shown in FIGS. 3 5. In this configuration,the thumbscrew 39 is rotated inwardly to fixedly interconnect the leg 27with the connecting bar 36. In this mode, the connecting bar 36functions to lock the legs 23 and 27 together. Since the linkages areall interconnected, all four legs 21, 23, 2S, and 27 are locked in afixed angular relationship with each other. In this configuration, thethumbscrew 51 is rotated outwardly to release the leg 27 from the flange49, and the thumbscrew 45 is rotated inwardly to fixedly connect theextension 43 and the hand grip 15 to the lever arm 21.

With the thumbscrews 39, 45 and 51 positioned as described, the four barlinkage is now capable of pivoting about the base support axis B. Thispivoting motion then imparts a reciprocating motion to the outputelement 40. Two angular positions of the four bar linkage movement areillustrated in FIG. 2 to show the movement of the hand grip 15 and thetransmitted movement of the output gimbal. This angular movement of thehand grip 15 can be accomplished by a driving movement of the operatorshand in a longitudinal direction.

The second configuration is shown in FIGS. 6 and 7. In thisconfiguration, the thumbscrew 51 is moved inwardly to fixedly connectthe leg 27 to the flange 49. Since the upper end of the leg 27 is alsorestrained against any lateral movement, the leg 27 is locked againstany movement. Moreover, the thumbscrew 39 is unscrewed to free the leg23 from the leg 27, while the thumbscrew 45 remains fixed to secure thehand grip 15 to the lever arm 21.

In this mode, the operator moves the hand grip 15 up and down in thedirections shown by pivoting his hand about his wrist located at axis C.The four bar linkage moves in a manner similar to a pantograph, i.e.,the lever arm 21 functions to pivot the legs 23 and 25 about the pivotpins 30 and 31 located on the fixed leg 27. The pivoting of the leg 23functions to pivot the con necting bar 36 (freed from the leg 27) aboutpivot pin 30. This pivoting movement is transmitted to the outputelement 40 to impart a reciprocating motion thereto. Again, two angularpositions of the four bar linkage movement is shown in FIG. 6. The typeof hand grip motion of this configuration is called the wrist pivotmotion and is preferred by many operators.

' The third configuration is shown in FIGS. 8 and 9. In thisconfiguration, both the thumbscrews 39 and 51 are screwed inwardly tolock the leg 23 to the leg 27; and the leg 27 to the flange 49,respectively. In this mode, the four bar linkage is then locked in afixed position.

The thumbscrew 45 is then unscrewed to enable the hand grip 15 to freelypivot with respect to the lever arm 21. After freeing the hand grip 15,the front extremity of the output element 40 is disconnected from theconnecting bar 36 and attached to the lower extremity of the extension43 with a connecting element 48.

In this mode, the operator pivots the hand grip about the axis A toimpart a reciprocating movement to the output element 40. Again, twoangular positions of this movement are shown in FIG. 8. This type ofhand grip motion is called the palm pivot motion because the operatormanipulates the hand grip 15 by pivoting the grip 15 about an imaginaryaxis through his palm.

As described above, either of the bores 53 and 55 can be utilized asconnecting points between the lever arm 21 and the leg 25. This not onlychanges the effective lengths of the legs but it also functions tochange the attitude and motion of the lever arm 21. Such an adjustmentis provided to again suit the operators preferences.

As can be seen, by making a few easy adjustments with thumbscrews, theside arm controller can be adjusted to function in three configurationsto accommodate any mode that the operator may wish to use.

It should be noted that various modifications can be made to theapparatus while still remaining within the purview of the followingclaims. For example, the relative effective lengths of any of the legsforming the quadrilateral can be different than that of thoseillustrated. Moreover, a plurality of bores similar to bores 53 and 55can also be formed on legs 23 and 27 to function in the same manner toadjust the configuration of the quadrilateral.

What is claimed is:

l. A mechanical linkage system comprising:

legs forming a four bar linkage pivotally interconnected at their endsto form a quadrilateral, said four bar linkage having a lever armforming one leg thereof, said four bar linkage further being con- Inected to a base at one of the corners opposite said lever arm;

an output element operatively connected to a leg adjoining said leverarm to be reciprocatingly driven thereby; and

means for adjustably locking certain of said legs with respect to theother legs and the base to vary the articulation of said lever arm.

2. The invention of claim 1 wherein said adjustment means comprisesmeans for locking the legs of said four bar linkage in a fixed angularrelationship with each other to enable the fixed four bar linkage topivot about the base support axis.

3. The invention of claim 2 wherein said means for locking the legs ofsaid four bar linkage in a fixed angular relationship with each othercomprises a connecting bar having removable attaching means forattaching said bar to two of said legs.

4. The invention of claim 3 wherein said-connecting bar forms a 90 angleand is positioned on said corner opposite said lever with the arms ofsaid bar extending along the adjacent legs.

5. The invention of claim 4 wherein said attaching means includes afirst connector element adapted to extend into a pair of mating boresformed on the leg opposite said lever arm and on the registering arm ofsaid bar.

6. The invention of claim 5 wherein said connector element is athumbscrew.

7. The invention of claim 1 wherein said adjustment means comprisesmeans for fixedly connecting the leg opposite said lever arm to saidbase to enable said lever arm to pivot the two legs adjoining said leverarm about their respective connecting points with said fixed leg.

8. The invention of claim 7 wherein said means for fixedly connectingsaid leg opposite the lever arm to said base comprises a pair of matingbores formed on said base and said opposite leg and a second connectorelement adapted to extend into said mating bores to interconnect the twocomponents.

9. The invention of claim 1 wherein said lever arm further comprises ahand grip pivotally mounted thereon, said hand grip having an extensionextending along said lever arm, said extension adapted to be alternatelyconnected to said output element to impart a reciprocating motionthereto.

10. The invention of claim 9 further comprising attaching means forconnecting said extension to said lever arm. I

11. The invention of claim 10 wherein said attaching means comprises apair of mating bores formed on said extension and said lever arm and athird connector element adapted to extend into said mating bores tointerconnect the two components.

12. The invention of claim 11 wherein said third connector elementcomprises a thumbscrew.

13.'A mechanical linkage system comprising:

legs forming a four bar linkage pivotally interconnected at their endsto form a quadrilateral, said four bar linkage having a lever armforming one leg thereof, said four bar linkage further being connectedto a base at one of the corners opposite said lever arm;

a hand grip pivotally mounted on said lever arm, said hand grip havingan extension extending along said lever arm;

an output element adapted to be alternately connected to a leg adjoiningsaid lever arm or to said extension to be operatively driven thereby;and

means for adjustably locking certain of said legs with respect to theother legs, the base, and the extension to vary the articulation of saidhand grip.

14. The invention of claim 13 wherein said adjustment means comprisesmeans for locking the legs of said four bar linkage in a fixed angularrelationship with each other to enable the fixed four bar linkage topivot about the base support axis.

15. The invention of claim 14 wherein said means for locking the legs ofsaid four bar linkage in a fixed angular relationship with each othercomprises a connecting bar having removable attaching means forattaching said bar to two of said legs.

16. The invention of claim 15 wherein said connecting bar forms a angleand is positioned on said corner opposite said lever with the arms ofsaid bar extending along the adjacent legs.

17. The invention of claim 16 wherein said attaching means includes afirst connector element adapted to extend into a pair of mating boresformed on the leg opposite said lever arm and on the registering arm ofsaid bar.

18. The invention of claim 17 wherein said connecting element is athumbscrew.

19. The invention of claim 13 wherein said adjustment means comprisesmeans for fixedly connecting the leg opposite said lever arm to saidbase to enable said lever arm to pivot the two legs adjoining said leverarm about their respective connecting points with said fixed leg.

20. The invention of claim 19 wherein said means for fixedly connectingsaid leg opposite the lever arm to said base comprises a pair of matingbores formed on said base and said opposite leg and a second connectorelement adapted to extend into said mating bores to interconnect the twocomponents.

21. The invention of claim 13 further comprising attaching means forconnecting said extension to said lever arm.

22. The invention of claim 21 wherein said attaching means comprises apair of mating bores formed on said extension and said lever arm and athird connector element adapted to extend into said mating boxes tointerconnect the two components.

23. The invention of claim 22 wherein said third connector elementcomprises a thumbscrew.

24. The invention of claim 1 further comprising means for varying theconnection point between any two legs to change the effective length ofeither leg.

25. The invention of claim 24 wherein said varying means comprises aplurality of bores formed in the two legs and a pivot pin extendingthrough any two bores of the two legs to pivotally interconnect the twolegs.

26. The invention of claim 13 further comprising means for varying theconnection point between any two legs to change the effective length ofeither leg.

27. The invention of claim 26 wherein said varying means comprises aplurality of bores formed in the two legs and a pivot pin extendingthrough any two bores of the two legs to pivotally interconnect the twolegs. l

1. A mechanical linkage system comprising: legs forming a four barlinkage pivotally interconnected at their ends to form a quadrilateral,said four bar linkage having a lever arm forming one leg thereof, saidfour bar linkage further being connected to a base at one of the cornersopposite said lever arm; an output element operatively connected to aleg adjoining said lever arm to be reciprocatingly driven thereby; andmeans for adjustably locking certain of said legs with respect to theother legs and the base to vary the articulation of said lever arm. 2.The invention of claim 1 wherein said adjustment means comprises meansfor locking the legs of said four bar linkage in a fixed angularrelationship with each other to enable the fixed four bar linkage topivot about the base support axis.
 3. The invention of claim 2 whereinsaid means for locking the legs of said four bar linkage in a fixedangular relationship with each other comprises a connecting bar havingremovable attaching means for attaching said bar to two of said legs. 4.The invention of claim 3 wherein said connecting bar forms a 90* angleand is positioned on said corner opposite said lever with the arms ofsaid bar extending along the adjacent legs.
 5. The invention of claim 4wherein said attaching means includes a first connector element adaptedto extend into a pair of mating bores formed on the leg opposite saidlever arm and on the registering arm of said bar.
 6. The invention ofclaim 5 wherein said connector element is a thumbscrew.
 7. The inventionof claim 1 wherein said adjustment means comprises means for fixedlyconnecting the leg opposite said lever arm to said base to enable saidlever arm to pivot the two legs adjoining said lever arm about theirrespective connecting points with said fixed leg.
 8. The invention ofclaim 7 wherein said means for fixedly connecting said leg opposite thelever arm to said base comprises a pair of mating bores formed on saidbase and said opposite leg and a second connector element adapted toextend into said mating bores to interconnect the two components.
 9. Theinvention of claim 1 wherein said lever arm further comprises a handgrip pivotally mounted thereon, said hand grip having an extensionextending along said lever arm, said extension adapted to be alternatelyconnected to said output element to impart a reciprocating motionthereto.
 10. The invention of claim 9 further comprising attaching meansfor connecting said extension to said lever arm.
 11. The invention ofclaim 10 wherein said attaching means comprises a pair of mating boresformed on said extension and said lever arm and a third connectorelement adapted to extend into said mating bores to interconnect the twocomponents.
 12. The invention of claim 11 wherein said third connectorelement comprises a thumbscrew.
 13. A mechanical linkaGe systemcomprising: legs forming a four bar linkage pivotally interconnected attheir ends to form a quadrilateral, said four bar linkage having a leverarm forming one leg thereof, said four bar linkage further beingconnected to a base at one of the corners opposite said lever arm; ahand grip pivotally mounted on said lever arm, said hand grip having anextension extending along said lever arm; an output element adapted tobe alternately connected to a leg adjoining said lever arm or to saidextension to be operatively driven thereby; and means for adjustablylocking certain of said legs with respect to the other legs, the base,and the extension to vary the articulation of said hand grip.
 14. Theinvention of claim 13 wherein said adjustment means comprises means forlocking the legs of said four bar linkage in a fixed angularrelationship with each other to enable the fixed four bar linkage topivot about the base support axis.
 15. The invention of claim 14 whereinsaid means for locking the legs of said four bar linkage in a fixedangular relationship with each other comprises a connecting bar havingremovable attaching means for attaching said bar to two of said legs.16. The invention of claim 15 wherein said connecting bar forms a 90*angle and is positioned on said corner opposite said lever with the armsof said bar extending along the adjacent legs.
 17. The invention ofclaim 16 wherein said attaching means includes a first connector elementadapted to extend into a pair of mating bores formed on the leg oppositesaid lever arm and on the registering arm of said bar.
 18. The inventionof claim 17 wherein said connecting element is a thumbscrew.
 19. Theinvention of claim 13 wherein said adjustment means comprises means forfixedly connecting the leg opposite said lever arm to said base toenable said lever arm to pivot the two legs adjoining said lever armabout their respective connecting points with said fixed leg.
 20. Theinvention of claim 19 wherein said means for fixedly connecting said legopposite the lever arm to said base comprises a pair of mating boresformed on said base and said opposite leg and a second connector elementadapted to extend into said mating bores to interconnect the twocomponents.
 21. The invention of claim 13 further comprising attachingmeans for connecting said extension to said lever arm.
 22. The inventionof claim 21 wherein said attaching means comprises a pair of matingbores formed on said extension and said lever arm and a third connectorelement adapted to extend into said mating boxes to interconnect the twocomponents.
 23. The invention of claim 22 wherein said third connectorelement comprises a thumbscrew.
 24. The invention of claim 1 furthercomprising means for varying the connection point between any two legsto change the effective length of either leg.
 25. The invention of claim24 wherein said varying means comprises a plurality of bores formed inthe two legs and a pivot pin extending through any two bores of the twolegs to pivotally interconnect the two legs.
 26. The invention of claim13 further comprising means for varying the connection point between anytwo legs to change the effective length of either leg.
 27. The inventionof claim 26 wherein said varying means comprises a plurality of boresformed in the two legs and a pivot pin extending through any two boresof the two legs to pivotally interconnect the two legs.